The present invention relates to an underpinning reinforcing means for foundations in civil engineering projects and buildings.
The underpinning strength of foundations in civil engineering projects and buildings is achieved by the peripheral base exerting a resistive force on the foundation when an external force is applied to the foundation. The present applicant has disclosed a foundation body and method of forming foundations, which increase underpinning strength in JP-A-5-40085.
In the disclosed method of forming foundations, as shown in FIGS. 8 and 9, a foundation body 1 disposes an additional reinforcing materials 3 comprised of bar steel in the periphery of a deep main foundation body 2. The additional reinforcing materials 3 extends radially from the deep main foundation body 2 in a horizontal sloping direction and is disposed plurally in the axial direction at fixed intervals. Each body is fixed into the peripheral natural ground 4.
The foundation body 1 is formed by the method outlined below. Firstly in order to form the main foundation body 2, the natural ground 4 is excavated in a fixed diameter and fixed depth in the vertical direction. A liner plate 6 is used to protect the excavation surface 7. Next the additional reinforcing materials 3 are fixed in the natural ground 4 from an opening portion 5 provided beforehand at a fixed position in the liner plate 6 in the order as shown in FIGS. 10-14. In other words, firstly boring into the natural ground 4 is performed from the opening portion 5 as shown in FIG. 10. As shown in FIG. 11, a hollow tube 9, for fixation of a tip and into which the additional reinforcing materials 3 is previously inserted, is inserted into a hole 8. The additional reinforcing materials 3 are longer than the hole 8 and the tip is expanded in a tapered shape to form a wedge 10. Furthermore the hollow tube 9 is constituted by a pipe body 11 and a fixing tube 12 which is freely attachable and detachable from the tip. The fixing tube 12, as shown in FIGS. 15 and 16, has a tapered portion 13 having the internal diameter of which is expanded toward the tip and a plurality of slits 14 formed in the axial direction from the tapered portion 13. After the additional reinforcing materials 3 and the hollow tube 9 are inserted, as shown in FIG. 12, an extraction force is applied to the additional reinforcing materials 3 while the presser tool 15 compresses the base side of the hollow tube 9. The fixing tube 12 is drawn into the natural ground 4 by the wedge 10 of the additional reinforcing materials 3 compressively expanding the tapered portion 13 of the fixing tube 12. Hence the additional reinforcing materials 3 cannot be detached. After this, as shown in FIG. 13, if a hardening agent 16 is poured while the pipe body 11 of the hollow tube 9 is cut and detached from the fixing tube 12, the additional reinforcing materials 3, as shown in FIG. 14, will leave a basal ends 17 which projects toward the center of the main foundation body 2 and will be fixed on all sides in the hole 8. In this way, the additional reinforcing materials 3 is fixed radially in the base in the horizontal and oblique direction at various depths.
Next while avoiding the basal ends 17 of the additional reinforcing materials 3 which projects from the natural ground 4, assembly of reinforcing rods of the main foundation body 2 is performed. After this, a fixed plate 18 is secured to basal ends 17 on the inner side of the reinforcing structure as shown in FIG. 17 and FIG. 18. The fixed plate 18 is welded to the axial reinforcing rod 19 and a lateral reinforcing rod 20 and the head of the basal ends 17 is secured to the fixed plate 18 by a fixing nut 21. As regards the additional reinforcing materials 3 which are disposed in an oblique direction in FIG. 8, a fixed metal element 18A, triangular in cross section such as that shown in FIG. 19, may be used instead of the fixed plate 18 to fix the basal ends 17. In this way, after securing the basal ends 17 of each additional reinforcing materials 3 to the reinforcing rods 19 and 20, the foundation body 1 as shown in FIGS. 8 and 9 can be formed by placing the concrete of the main foundation body 2.
In a foundation body 1 formed in this way, the additional reinforcing materials 3 is strongly integrated with the natural ground 4 due to the adhesive force of the hardening agent 16 plugging the periphery and the securing force to the natural ground 4 as a result of the wedge 10 resisting detachment. Thus the base in the periphery of the additional reinforcing materials 3 is strengthened. On the other hand, the basal ends 17 is rigidly attached to the main foundation body 2 due to being fixed to the reinforcing rods 19 and 20 of the main foundation body 2. As a result, the foundation body 1 functions as a single foundation containing a peripheral base 22. The surface on which shear resistance s acts when an extraction force Fv acts on the main foundation body 2 is the imaginary underpinning surface 23 connecting the tip of each additional reinforcing materials 3 as shown in FIG. 20. Hence the surface area on which shear resistance s acts is conspicuously expanded and the underpinning strength with respect to an extraction force is greatly increased.
Furthermore the underpinning structure with respect to a horizontal force Fh is strengthened as shown in FIG. 21. In other words, the surface on which the passive earth pressure p1 and the elastic base reactive force p2 act is expanded to an imaginary support surface 24 of the semicircular cross section connecting the tips of each additional reinforcing materials 3 which are disposed in the left half of the main foundation body 2 in the figure. Thus since the base 22 is strengthened by the additional reinforcing materials 3, the range of the layers of earth B which obtain the elastic base reactive force p2 is expanded in the upward direction. The resistance a of the additional reinforcing materials 3, which is disposed in the right middle half of the figure of the main foundation body 2, acts as an underpinning force with respect to extraction forces. Therefore the foundation body 1 obtains an extremely strong underpinning force with respect to horizontal forces Fh.
However in this type conventional foundation body and method for forming foundations, since there is no accurate standard for the method of placement of the additional reinforcing materials 3 with respect to the foundation body 1, in other words the extension of the additional reinforcing materials 3, it is not always possible to obtain a sufficient application of the reinforcing underpinning due to the additional reinforcing materials 3. In other words, in foundations such as those of high voltage electricity towers for example, underpinning forces with respect to extractive forces are more of a problem than compressive forces. However even if it is attempted to create reinforced underpinning forces which resist a detaching force on the foundation body 1, it has not been possible to create an accurate method of placing the additional reinforcing materials 3.
The present invention is proposed to solve the above problems and has the objective of providing a foundation body and method of disposing an additional reinforcing material in foundations with a reinforced base which obtains a reinforced underpinning force especially with respect to detaching loads.
The present invention provides a method of forming foundations with a reinforced base by boring into the earth from the excavation surface of the foundations. After a highly rigid additional reinforcing material is fixed into the bore, the base of the additional reinforcing material is fixed to the main foundation body and the main foundation body is formed. The resistance of the foundation body with respect to tensile forces is strengthened by the structural apportioning by the additional reinforcing material of a part of the shear stress and the tensile stress with respect to the earth. Thus for each additional reinforcing material:
xcex94pr=(Nmax. cos"THgr")+Smax. sin"THgr"). tan"PHgr"
where Nmax is the maximum axial force of the additional reinforcing material, Smax is the maximum shear force of the additional reinforcing material, "THgr" is the angle of placement of the additional reinforcing material, "PHgr" is the inner frictional angle of the base.
As a result, the total reinforcing effect xcex94p which expresses the underpinning strength of the foundation body is the result of the increase in the resistance xcex94ps due to the structural effect generated by the structural apportioning by each additional reinforcing material itself of a part of the tensile stress and the shear stress with respect to the earth and the increase in the resistance xcex94ps due to the effect of the reinforcing effect which is expressed as
xcex94p=xcex94ps+xcex94pr
In the present invention, as the additional reinforcing material is disposed so as to maximize the increase in the resistance xcex94pr, the total reinforcing effect xcex94p increase due to the increase in the confining pressure with respect to the foundation body increases. Thus the foundation body is supported in an extremely strong manner in the earth.
Thus the present invention is effective for use in high voltage electrical towers which entail the problem of underpinning strength withstanding detaching forces. While keeping the foundation body to small dimensions, the underpinning strength due to the reinforcing effect is conspicuously improved. Hence the cost of the foundation construction is greatly reduced, the time required is reduced and the amount of earth removed due to boring is reduced.
Furthermore the present invention provides a method of forming foundations with a reinforced base by boring into the earth from the excavation surface of foundations. After a highly rigid additional reinforcing material is fixed into the bore, the base of the additional reinforcing material is fixed in the foundation body thus forming the main foundation body. The additional reinforcing material may be a bar shaped body. The orientation of the additional reinforcing material is made to correspond with the direction of minimum principal strain in the earth which is the direction in which the tensile axial force of the additional body is at a maximum when a detaching force acts on the foundation body.
Furthermore, this invention provides foundation bodies with a reinforced base constructed from a main foundation body constructed after boring in the earth and additional reinforcing materials which extend in a radial direction from the foundation main bodies. The additional reinforcing materials have a bar shape and have a downward angle of inclination with respect to the axial direction of the main foundation body so that their orientation corresponds to the direction of minimum principal strain in the earth which is the direction in which the tensile axial force of the additional reinforcing material is at a maximum when a detaching force acts on the foundation body.
As a result, the base is strengthened by a plurality of additional reinforcing materials fixed in the earth. Also the base is integrated with the main foundation body as the base part of the additional reinforcing material is fixed to the main foundation body. As a result, the underpinning strength of the foundation body is increased by the structural effect generated by the additional reinforcing material itself structurally apportioning a part of tensile and shear stress with respect to the earth and by the reinforcing effect confining the tensile strain generated by the earth and increasing the rigidity of the entire base. The reinforcing effect is to greatly limit the tendency of the earth to expand and to limit the absolute value of the increase in minimum principal strain during shear fracture of the earth by the additional reinforcing materials which pull the earth in the periphery of the foundation body. The reinforcing effect is also generated by an increase in minimum principal stress. However the effect of the additional reinforcing materials of the present invention drawing the peripheral earth toward the foundation body when a detaching force acts on the foundation body is maximized by their orientation in the direction of minimum principal strain in the earth in the periphery of the foundation body. Therefore in accordance with the present invention, the reinforcing effect as a result of the additional reinforcing materials is maximized. Hence since shear strength with respect to maximum principal stress is increased and the base in the periphery of the foundation body is strengthened, the confining pressure with respect to the foundation body is increased and the foundation body is strongly underpinned by the earth.
Thus the present invention may be employed in high voltage electricity towers which suffer from the problem of underpinning strength with respect to detaching forces. While maintaining small dimensions for the foundation body, the underpinning strength attributable to the reinforcing effect is conspicuously increased. Hence the cost of foundations is greatly reduced, the time required for their placement is reduced and to the degree the foundation body is reduced in size, the amount of extracted earth is reduced.
The present invention is provided with a plurality of additional reinforcing materials which are disposed at roughly equal intervals in the entire periphery of the outer circumference of the main foundation body. As a result it is possible to obtain a high underpinning strength by the additional reinforcing materials.
The additional reinforcing materials of the present invention are approximately ⅔ the length of the diameter of the main foundation body. With these dimensions, it is possible to obtain a high underpinning strength by the additional reinforcing materials.
The additional reinforcing materials of the present invention are disposed at a ratio of one for every 3 square meters in the outer surface of the main foundation body. In this way, maximum efficiency of degree of reinforcement with respect to the number of additional reinforcing materials used can be achieved.
Furthermore foundation main bodies which have a short length in the radial direction are used in the present invention. The additional reinforcing materials are disposed stepwise in the axial direction of the main foundation body. The present invention affords a sufficient strengthening effect with respect to foundations of such a short length.